Fix long case blocks not split into multiple lines

CHANGES.md

@@ -12,6 +12,8 @@
 - Fix crash when whitespace followed a backslash before newline in a docstring (#4008)
 
 - Fix crash on formatting code like `await (a ** b)` (#3994)
+- Fix a bug that long `case` blocks will not be split into multiple lines, also enabled
+  general trailing comma rules on `case` blocks (#4024)
 
 ### Preview style
 

src/black/linegen.py

@@ -1260,6 +1260,13 @@ def normalize_invisible_parens(
                 child, parens_after=parens_after, mode=mode, features=features
             )
 
+        # Fixes a bug where invisible parens are not properly wrapped around
+        # case blocks.
+        if isinstance(child, Node) and child.type == syms.case_block:
+            normalize_invisible_parens(
+                child, parens_after={"case"}, mode=mode, features=features
+            )
+
         # Add parentheses around long tuple unpacking in assignments.
         if (
             index == 0

tests/data/cases/pattern_matching_extras.py

@@ -30,22 +30,6 @@ def func(match: case, case: match) -> case:
             ...
 
 
-match maybe, multiple:
-    case perhaps, 5:
-        pass
-    case perhaps, 6,:
-        pass
-
-
-match more := (than, one), indeed,:
-    case _, (5, 6):
-        pass
-    case [[5], (6)], [7],:
-        pass
-    case _:
-        pass
-
-
 match a, *b, c:
     case [*_]:
         assert "seq" == _
@@ -71,12 +55,12 @@ def func(match: case, case: match) -> case:
     case [a as match]:
         pass
 
-    case case:
+    case anything:
         pass
 
 
 match match:
-    case case:
+    case something:
         pass
 
 

tests/data/cases/pattern_matching_generic.py

@@ -25,9 +25,9 @@ def get_grammars(target_versions: Set[TargetVersion]) -> List[Grammar]:
         ]
 
     match match:
-        case case:
+        case something:
             match match:
-                case case:
+                case something:
                     pass
 
     if all(version.is_python2() for version in target_versions):

tests/data/cases/pattern_matching_long.py

@@ -0,0 +1,39 @@
+# flags: --minimum-version=3.10
+match x:
+    case "abcd" | "abcd" | "abcd" :
+        pass
+    case "abcd" | "abcd" | "abcd" | "abcd" | "abcd" | "abcd" | "abcd" | "abcd" | "abcd" | "abcd" | "abcd" | "abcd" | "abcd" | "abcd" | "abcd":
+        pass
+    case xxxxxxxxxxxxxxxxxxxxxxx:
+        pass
+    case case:
+        pass
+
+# output
+
+match x:
+    case "abcd" | "abcd" | "abcd":
+        pass
+    case (
+        "abcd"
+        | "abcd"
+        | "abcd"
+        | "abcd"
+        | "abcd"
+        | "abcd"
+        | "abcd"
+        | "abcd"
+        | "abcd"
+        | "abcd"
+        | "abcd"
+        | "abcd"
+        | "abcd"
+        | "abcd"
+        | "abcd"
+    ):
+        pass
+    case xxxxxxxxxxxxxxxxxxxxxxx:
+        pass
+    case case :
+        pass
+

tests/data/cases/pattern_matching_trailing_comma.py

@@ -0,0 +1,39 @@
+# flags: --minimum-version=3.10
+match maybe, multiple:
+    case perhaps, 5:
+        pass
+    case perhaps, 6,:
+        pass
+
+
+match more := (than, one), indeed,:
+    case _, (5, 6):
+        pass
+    case [[5], (6)], [7],:
+        pass
+    case _:
+        pass
+
+
+# output
+
+match maybe, multiple:
+    case perhaps, 5:
+        pass
+    case (
+        perhaps,
+        6,
+    ):
+        pass
+
+
+match more := (than, one), indeed,:
+    case _, (5, 6):
+        pass
+    case (
+        [[5], (6)],
+        [7],
+    ):
+        pass
+    case _:
+        pass